I'd like to gen up another world, but am a little deterred from doing so with all of the big changes coming out. Will these upcoming bugfixes be compatible with 0.34.05-made saves?
Well, Toady said that the problem with incompatible saves for v0.34.01 vs v0.34.02+
should be a one time thing, but there is a small chance that some bugfix may force that to happen again. I'd pretty much bet that the rest of the v0.34.x tree should be backwards compatible with v0.34.02 and higher saves though.
On the other hand, there may be some changes in world gen or such that will solve various problems, but you will only see the fix if you regenerate your world or do some file editing. Most of these are probably going to be minor inconveniences at this point, but I'd give this a higher probability of having a fix you want. If you're OK with that though, then go ahead and start playing now.
Or, you could just do what I did, and start a fortress now to just screw around and try some stuff without worrying about all of the stuff you normally would, just so you won't be so rusty when the well-enough-debugged-for-you version is released. I'm playing around with breaching aquifers now, which was something I had avoided previously, and trying various kinds of squad training. (Meanwhile the rest of my fortress is
way behind where it would normally be at this point in the game.
)